The invention relates to the field of the recovery of distorted optical images.
Restorations of images from turbulence aberration and blur are important problems in signal processing. While many computer algorithms have been developed for these purposes, these algorithms were beneficial in solving problems with quantified and non-quantified sources of distortion. These algorithms are very difficult to implement optically and their execution is not real time. Therefore, optics remains confined to solve distortion problems where the distortions is well quantified and measured. The origins of these distortion can be the following: misfocussing, motion, lens aberration and distortion through transmission in thin aberrating media. It is well-known that in order to recover those types of distorted signals, one is required to performed deconvolution or exact phase compensation. Unfortunately, up to now, there is no optical system which can be used to solve problems with unknown distortion as in the case of blind deconvolution. In digital processing, deconvolution of the blurred image by the blurring function is a straightforward problem. However, optically this is an extremely difficult task due to the difficulties in the fabrication process of the inverse filter. Therefore, in accordance with the present invention, we provide a pseudo deconvolution technique wherein we replace the exact phase of the inverse filter (the Fourier transform of the blurring function) by its phase coded filter and we replace the amplitude of the inverse filter by its amplitude statistical distribution.
Recovery of distorted images, which have passed through thin or thick aberrating media, has been demonstrated in many scientific papers. The majority of the techniques for recovering the signal from a thick aberrating medium rely on double-pass methods using phase conjugate mirrors which means that they will have very limited application. There were also some attempts for one-way image transmission through thin aberrating media.
While some of these techniques were purely based on phase conjugate means, some others were based on the combination of the phase conjugate techniques and the opto-electronics devices or purely opto-electronics. Generally, the performance of aberration correction using phase conjugate means was poor for two main reasons. The first reason is related to the nature of writing efficient gratings in real time holographic media. Because the receiving channel is always at an angle with the casting channel, the projection from the casting channel to the receiving channel is always accompanied by losses in the resolution. The second reason is related to the weak intensity of the distorted signals. It is well-known that due to the current limitation on the available materials, phase conjugators are slow or don't respond to low light intensities.
Opto-electronics techniques also have their limitations. These techniques usually require spatial light modulators that can address phase information. Unfortunately, there are very few such spatial light modulators existing today. In addition, they are expensive. Therefore, we propose and evaluate several simple signal recovery techniques which are based on phase and/or amplitude coding filters. These techniques can be implemented by all of the available spatial light modulators (binary phase, binary amplitude, ternary amplitude or phase, continuous amplitude or phase). Since the method of the present invention does not use the exact phase information of the distortion function, our results are always accompanied by some degree of additive noise. The additive noise in the recovered image is dependent on the specific recovery coding techniques used and how they are implemented.